Broad band contactor assembly for testing integrated circuit devices

ABSTRACT

A contactor assembly for testing electronic devices that are packaged with a dual-in-line pin array has an insulating base that mounts two rows of contacts, each adapted to flex into electrical connection with a pin of the device, and a pair of flexible ground planes each spaced closely from an associated one row of said contacts. A flexible, insulating spacer maintains the ground planes and their associated row of contacts with a substantially fixed spacing there between during the flexural movement of said contacts. In the preferred form, the upper edge of the ground planes adjacent the pins includes an arrangement for securing a chip electronic device, a capacitor or a resistor. The other end of the chip mounts a contact tip that makes electrical connection with an associated pin when the associated contact also connects with the pin. The signal path provided by the holder, chip and tip is extremely short, preferably less than 0.150 inch. The contacts and ground planes electrically surface mount on a contactor board. Flexible lower end portions of the contacts and ground planes make direct electrical connection with signal pads and ground planes on the board without the use of connectors. A flexible mount formed by strips of a conductive material having arms soldered to two or more contacts hold a surge capacitor that decouples the device from ground noise during large current surges.

This application is a continuation of application Ser. No. 088,894,filed Aug. 24, 1987, abandoned which is a continuation of Ser. No.660,475, filed Oct. 12, 1984, now U.S. Pat. No. 4,689,556.

BACKGROUND OF THE INVENTION

This invention relates in general to testing apparatus for electronicdevices. More specifically it relates to a contactor assembly that isgenerally frequency insensitive to allow broad band testing ofintegrated circuits with fast-rising signals and has a connection andmounting system that is reliable and easy to use.

In the manufacture and use of integrated circuits (IC's) and similarelectronic devices it is important to test the devices accurately,reliably and at a high rate. Automatic testing and handling apparatusmachines that can perform this task are available. Such apparatussuitable for testing dual-in-line packaged (DIP) IC's are sold by theDaymarc Corporation, Waltham, Mass., under the trade designation Types1157 and 757. In a DIP device, the circuit is contained in a moldedplastic body having a generally rectangular, box-like configuration. Tworows of generally parallel connecting pins are arrayed along parallelsides of the body with each pin extending in a direction generallynormal to the main faces of the body.

In each of the aforementioned apparatuses the IC's are momentarilybrought to rest at a test station where a set of contacts, typicallydouble Kelvin contacts, are flexed by a push bar action into electricalconnection with the pins of the device under test (DUT). The contactsestablish an electrical connection between testing circuitry and thedevice. The contacts are usually part of a probe or contactor assemblywhich includes an insulating base member that mounts the contacts. Thecontacts are typically narrow strips of a resilient and highlyconductive material. The contacts typically make electrical connectionwith an associated connecting pin at a free end opposite the base. Thecross-sectional dimensions of the contacts are relatively small due to(1) the requirement that all of the contacts simultaneously makeconnection with a set of closely packed pins and (2) the requirementthat the contacts flex for millions of cycles of operation withoutmaterial fatigue. The length of the contacts is determined by thespacing between the test station of the IC handling apparatus and thetest circuitry.

Frequently the testing of the integrated circuits requires that thetesting signal be "fast-rising", that is, a signal which is a verysteep, step-like increase in potential. A typical fast-rising signal ischaracterized by a voltage change of 5 volts per nanosecond. Such asignal can be represented through Fourier analysis as being composed ofa multitude of superimposed sine waves having a very high frequency,typically on the order of 300 MHz. The fast-rising signal launched bythe test circuitry and carried by the contacts to the device thereforecontains components with very high frequencies.

A major problem with this testing arrangement is that due to theinherent inductance of the contacts themselves, the signal encounters aninductive reactance X_(L). This reactance produces distortions andreflections which degrade the quality and accuracy of the test. Theinductance L of the contact is a function of the cross-sectional area ofthe conductor and its length. Inductance increases directly with thelength and inversely with the cross-sectional area. Since the inductivereactance X_(L) =2πfL, for the very high frequencies f associated with afast-rising signal, the inductive reactance associated with even therelatively short contacts in normal use becomes a significant source ofdistortion and limits the accuracy of measurements.

One possible solution would be to increase the cross-sectional area ofthe contacts. However, the physical constraints of the test environmentlimit the useful dimensions of the contacts. For example, the contactsmust be separated laterally from adjacent contacts while stillmaintaining a unique association with one pin on the IC. Also, thecontacts must be sufficient thin to flex repeatedly without exhibitingfatigue. Another possible solution is to make the contacts shorter. Thissolution works well if the IC can be placed manually into the testcircuit. However, with high speed automated operation (e.g. 6,000 unitsper hour), the test circuitry must be physically separated from thedevice handling mechanisms with electrical connection made over someshort distance spanned by a probe or contactor assembly of the typedescribed above. In short, modern production economics require contactshaving a length which is troublesome for fast-rising signals. Anotherpossible solution is simply to test each device more slowly to wait fordistortions and reflections to die out. With many modern IC's, however,the speed of operation of the device itself is so fast that if thetesting operation were to extend over a sufficient period of time toallow distortions and echoes induced by the fast-rising testing signalto subside, then the speed rating of the devices cannot be determined.In short, the testing operation must have a speed comparable to that ofthe device function being tested.

Another consideration is minimizing "ground noise", that is, changes inthe reference voltage due to current surges during the test proceduresimulating operation of the device. A typical situation is a test wherea change in the device state causes a current surge in the range of 20milliamperes per nanosecond. Such a surge can cause the ground referenceto move 1 volt or more thereby distorting measurements referenced toground by 20% or more. The end result is that good devices may not passthe test and are downgraded.

Another problem with testing apparatuses for electronic devices existsin the way the probe or contactor assemblies are connected to a testcircuit. When there is a high density of electrical contacts in aconfined area, it is difficult to make connections with the testingcircuitry while maintaining signal fidelity. The use of connectorstypically introduces discontinuities which introduce reflections.

The interface assembly taught by Daymarc Corporation's U.S. Pat. No.4,473,798 is one type of connection that avoids this disadvantage. Itprovides the necessary high density, characteristic impedance multipleelectrical connections to multiple contacts and ground plates. It usesinterchangeable contactor assemblies replaceably mounted on contactorboards. A pattern of conductive stripes is carried on at least one faceof the board. Elastomeric connectors with narrow, mutually spaced apartconductive filaments electrically connect the stripes with the contactsand plates of the contactor assembly. The contactor board is clamped tothe test contactor assembly at its rear surface to establish a uniqueelectrical connection between each conductive stripe and an associatedcontact or plate.

While this interface assembly offers a much improved flexibility overprior connectors, under factory operating conditions there has been somedifficulty in maintaining the conductive stripes of the elastomericconnectors aligned with the conductive stripes of the contactor board.It is also significant that the contactor assembly is assembled to thecontactor board from the rear side and then mounted on a handler. Thetest circuit is then brought up and connected to the contactor board.With this arrangement, after the electrical connections through theboard and the contactor assembly are tested, signal lines must be brokenand re-established in order to operate the test system with atest/handler.

A further problem with the contactor assembly described in theaforementioned Daymarc '798 patent as well as U.S. Pat. No. 4,419,626 isthat while a surge capacitor is connected across two pins in parallelwith the device being tested to provide power-ground decoupling forfast-rising current surges, this location is far enough removed from thedevice that significant ground noise remains. Also, in certain testsituations it is desirable to be able to connect certain pins to oneanother during the test so that they are at the same potential andotherwise are in the same electrical condition. With existing contactorassemblies, there has been no convenient way to short out two or moreDUT pins over a short signal path that will not itself introducereflections and distortions, particularly where the test signal has veryhigh frequency components.

In U.S. Pat. Nos. 4,419,626 and 4,473,798, assigned to the assignee ofthe present invention, a contactor assembly is disclosed which iscapable of testing electronic devices including high-speed ICs, withoutpresenting significant inductive reactance to a fast-rising signallaunched in any contact of the assembly. This test contactor assemblyincludes at least one row of flexible contacts which are secured at oneend to an insulated base. A conductive plate, also secured to the base,extends to a generally parallel, closely spaced relationship to each rowof contacts. The dimensions of the plate and its spacing from theassociated contacts produce a distributed capacitance with respect toeach contact in the row so that a fast-rising test signal launched in acontact encounters a purely resistive or "characteristic" impedance thatis frequency independent.

While the contactor assembly of U.S. Pat. No. 4,419,626 gives excellentelectrical performance, it does not solve the problem of reflections anddistortions produced at the connection between the contact and a pin ofthe IC, nor does it isolate the signal on one contact from electricaldistrubances produced by changes in the electrical state of the DUT. Thetest signal is transmitted to the device over the contacts which have apreselected "characteristic" impedance, typically in the range of 50 to100 ohms. If the device is a 50 ohm device and the characteristicimpedance of the contacts is also 50 ohms, then the transition from thecontactor assembly to the device is smooth. If, on the other hand, thedevice has a high impedance, then the transition from a 50 ohm contactorassembly to the device results in signal reflections and signaloscillation. With this system, the device under test cannot be decoupledadequately from the test fixture and the quality of the signal seen bythe device becomes uncertain. This reduces the reliability of the test.

It is also quite important to note that ideally a test fully simulatesthe electronic and physical environment that the DUT is likely toencounter when it is eventually used as a component of a circuit.Existing test systems have not been able to fully duplicate actual useconditions, in part because they have not been able to produceconnections in a high speed test environment where a DUT pin isconnected to ground over a very short signal path, as is often the casein an actual circuit, which may include capacitive or resistive circuitelements. Another shortcoming of existing contactor assemblies is thatcharacteristic or matched impedance signal lines usually terminate in animpedance mismatch, not the characteristic impedance. It is desirable tobe able to terminate a signal line in the characteristic impedance (e.g.50 ohms) to substantially eliminate signal reflections. It is alsoimportant, if one wishes to simulate a variety of end-use circuitenvironments, to be able to vary the electronic test characteristics atselected DUT pins, that is, to configure and reconfigure the testenvironment readily and in the field. Prior art contactor assemblies donot provide this capability while also meeting the other desiredoperating characteristics enumerated above.

It is therefore a principal object of the present invention to providean improved characteristic impedance contactor assembly for testingelectronic devices.

Another significant object is to provide an improved contactor thatdecouples, or terminates in the characteristic impedance, individualpins of the device under test (DUT) through an electrical path lengthwhich is equivalent to the distance recommended for a final operativecircuit for the device.

Another object of the invention is to provide this decoupling ortermination in the characteristic impedance selectively at a pin or pinsof the device under test.

Another object is to provide power-ground coupling that is solderconnected, low impedance and close to the device.

Another object of the invention is to provide a contactor assembly thatelectrically connects to a contactor or DUT board with a high degree ofreliability and convenience and eliminates connectors or soldering.

Yet another object of the invention is to provide a contactor assemblythat surface mounts to a contactor or DUT board from its front sideadjacent the device under test so that testing of the contactor assemblyto board connections does not require that signal lines be broken andthen re-established to begin production testing of devices.

Another object is to provide a contactor assembly where a power-groundplane can serve as a shorting bar between two or more pins.

A further object is to provide a contactor assembly that can be fieldconfigured, or reconfigured, to the testing requirements of a deviceunder test and which can be field maintained.

Another object of the invention is to provide a contactor assembly withthe foregoing advantages that has a generally simple, low cost, andhighly durable construction.

SUMMARY OF THE INVENTION

A contactor assembly for electronic devices, particularly dual-in-linepackaged (DIP) IC's with two parallel rows of connecting pins, has aninsulating base that supports at least one row of resilient electricalcontacts. A distinctive feature of the present invention is that thelower ends of these contacts pass through the base and terminate inflexible end portions which are designed to make electrical connectionwith signal pads of a test circuit board. In a preferred form theflexible end portions, or "feet," are bent into a V-shaped configurationand the signal pads are in direct connection with plated through holesthat reach an internal conductive strip uniquely associated with thatsignal pad, and hence that contact. The upper ends of the contact extendin a generally perpendicular direction from the base, and these upperends are typically angled toward an associated pin to make electricalconnection with the pin when the contact is flexed toward the device.Each contact has small cross section that is designed to conduct anelectrical signal along its length between test circuitry and the devicebeing tested. Each contact is structured to flex resiliently from afirst non-testing position where the upper end of the contact is spacedfrom its associated pin to a second testing position where the upper endis forced into electrical connection with the pin.

The base also supports a plate, which serves as a ground plane and whichis associated with and oriented in a generally parallel, closely spacedrelationship with respect to each row of the contacts. The spacing ispreferably uniform and is maintained by a layer of flexible insulatingmaterial which is inserted between each of the rows of contacts and theassociated plate. The plate is continuous and extends substantially thefull length of the associated row. The plate terminates at its lower endin a plurality of flexible contacting end portions, preferably alsoV-shaped "feet", which make electrical connection to a conductive groundsurface on the test board. The flexible feet and contactor boardconnection system allows the contactor assembly to be surface mounted ona "device under test"]or DUT board without additional connectionelements and thus reduces signal distortion.

The relative dimensions of the contacts, the associated plates and theinsulation layer are adjusted to produce a distributed capacitance asseen by a signal transmitted along the contacts. The value of theresulting capacitive reactance substantially offsets the inductivereactance produced by the self inductance of the contacts. As a result,a fast-rising signal launched in a contact encounters a substantiallycharacteristic impedance.

A principal feature of the present invention is that the upper end ofthe plate terminates in a plurality of chip holders which are designedto secure one end of a small chip capacitor or resistor. The oppositeend of each chip mounts a contact tip that makes electrical connectionwith an associated pin of the device being tested. In the preferredform, a holder is associated with each of the contacts of the contactorassembly. With this holder-chip contact tip structure any DUT pin can beterminated to ground through the chip over a path that is typically lessthan 0.150 inch.

A further feature of the contactor assembly of this invention is asystem for mounting a surge capacitor very near the device and inparallel between two diagonally opposite power pins, or between groupsof pins. The mounting system includes two strips of a flexibleconductive material that are suspended just below the device by a pairof arms or multiple arms that are soldered or otherwise secured to thecontacts associated with the power pins. The strips are separated fromone another with the surge capacitor bridging them. In theimplementations illustrated, the strips are virtually in one plane,however, the strips can be in multiple planes with the chip capacitorforming the connection between the planes.

These and other features and objects of the invention will be moreclearly understood from the following detailed description of thepreferred embodiments which should be read in light of the accompanyingdrawings.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a perspective view of the contactor assembly of the presentinvention mounted to a contactor board;

FIG. 2 is a perspective view of the contactor assembly shown in FIG. 1with its contacts and ground plates flexed into electrical connectionwith the pins of an IC;

FIG. 2A is a detail of one chip device, its holder formed integrallywith a ground plane, and a contact tip;

FIG. 3 is an exploded perspective view of the contacts ground plates andinner spacers of the contactor shown in FIGS. 1 and 2;

FIG. 4 is an unexploded perspective view of the contactor assembly shownin FIG. 3 but with the flex rods in place;

FIG. 5 is a view in vertical section of the contactor assembly shown inFIG. 2;

FIG. 6 is a simplified view in vertical section of the contactorassembly shown in FIG. 2;

FIG. 7 is a detailed perspective view of the mounting system for thesurge capacitor shown in FIGS. 2, 5 and 6;

FIG. 8 is a top plan view of the contactor board shown in FIG. 1; and

FIG. 9 is a cross-sectional view taken along lines 9--9 of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1-4 show a test contactor assembly 12 having two rows 16a, 16b ofcontacts 16 and a pair of conductive plates 18a, 18b which each serve asa ground plane 18. For the purpose of this description, the plates androws of contacts are taken as being vertically oriented. Each plane 18is associated with one row of contacts 16. Each contact 16 extendsthrough a longitudinal slot 27 in a base 14. An upper end 22 of eachcontact 16 is angled toward an associated pin 24 of an integratedcircuit (IC) 26. A lower end of each contact 16 terminates in a V-shaped"foot" 16f. The lower end of each plate 18 terminates in a plurality oflongitudinally spaced V-shaped "feet" 18f. Each plane 18 preferablyincludes the same number of feet 18f as the number of contacts 16 withwhich the plane 18 is associated. The cross-section of each contact 16is preferably generally rectangular with the broad face of each contactparallel to the pins 24.

The base 14, which is most clearly shown in FIG. 5, includes theopenings 27 that receive the contacts 16 and the planes 18. Within theopenings 27, the lower ends 20 of the contacts 16 are spaced from theirassociated plane 18 by flexible insulating strips 28a,28b made ofmaterials such as fluoroplastic which extend substantially along theentire height of the contacts 16. Insulating strips 30a,30b which extendfrom the lower end 20 of the contacts 16 to the upper end of the base14, space the contacts 16 from the base 14 and clamp the contacts andplates in the desired vertical orientation when screws 31,31 passthrough the contactor assembly and thread into holes in a portion 14c ofthe base 14. A mirror image base portion 14a lies on the opposite sideof the contacts and ground plates. A middle portion 14b sets the spacingbetween the contact rows 16a and 16b.

The base 14, which is preferably made from a structurally stableinsulating material such as an epoxy fiberglass, has its rear or lowerface abut a device under test (DUT) or "contactor" board 34. This board,one form of which is shown in FIGS. 8 and 9, includes a plurality ofindividual electrical signal pads 36 arrayed in two rows 37 contactregions 38 of a ground plane positioned adjacent, but spaced from, therows 37. The lower end of the base 14 includes two longitudinallyextending cavities 32,32 that each overlie one row 37 of the electricalsignal pads 36 portion of one of the ground plane regions 38. Thecontacts 16 and planes 18 make contact with these electrical signal pads36 through V-shaped feet 16f and 18f. The feet 16f are spaced from eachadjacent foot 16f, each foot can connect with only one electrical signalpad 36. To connect to a test circuit, in one form illustrated, thesignal pads each connect to a conductive strip 39 within the boardthrough a plated through hole 39a of conventional construction. Theinternal conductive strips extend to other signal pads at the peripheryof the board 34 to facilitate connection to a test circuit. Otherarrangements, such as direct coaxial wires attached to conductivestripes, are also possible. What is significant is that with the presentinvention the contactor assembly mounts on a surface with signal pads,that the signal is brought to the pad on a matched impedance line, andthat the system uses no connectors that can introduce signaldistortions. It is also significant that once the contactor assembly,contactor board, and test circuit are assembled and electricallyconnected, they can be mounted on a test/handler as a unit withoutbreaking signal lines. One mounting system, as illustrated, uses pins35, 35 that project from the contactor assembly, locate the assembly onthe test/handler, and are secured by cam plates (not shown).

The contacts 16 and the planes 18, as well as the electrical signal padcontacting feet 16f, 18f, are formed of a material which is resilientand resistant to material fatigue. In the preferred embodimentillustrated, the feet 16f, 18f initially extend in a generally verticaldirection from the associated contact 16 or plane 18 and they terminatein the aforementioned V-shaped end. The V-shaped foot of the contact 16is oriented in a direction opposite that of the free end of thecorresponding foot 18f of the adjacent plane 18. This orientationenables the contacts 16 and the planes 18 to be placed in closeproximity to each other while maintaining reliable electricalconnections at the board 34.

As the contactor assembly 12 is mated to the electrical board by screws33,33, the feet 16f contact the signal pads 36. As the screws aretightened, the feet 16f "flatten out" in the direction of their freeend. This flexing or "flattening out" is controlled by the size of thecavities 32 in the base 14 in relation to the size of the fact 16f or18f. If the cavities 32 are shallow, a larger compressive force isdeveloped than with a deeper cavity.

In their normal unflexed position shown in FIGS. 1 and 3-4, the contacts16 and planes 18 are generally perpendicular to the base 14. In thisposition, the ends 22 of the contacts are spaced from the pins 24. Thecontacts 16 and plane 18 are placed in the testing position (FIGS. 2 and5-6) by a lateral force (typically delivered by a push bar) acting oninsulating rods 46,46 which are held at the outer face of planes 18a,18bby rod supporting members 46. The planes 18 and insulating layers28a,28b should therefore be sufficiently flexible so that they do notsignificantly impede flexural movement under the lateral force.

A row of mutually spaced apart, C-shaped chip holders 40 are formed onthe upper end of plane 18. The number of holders 40 corresponds to thenumber of contacts 16 in a row. The holders 40, best seen shown in theinset of FIG. 2, include upper, lower and rear walls which secure asmall chip capacitor or resistor 42 so that it extends from the pocket40 towards a pin of the device being tested. The chip end is inelectrical connection with the holder and is typically soldered. Aconnection member 44 fits on the opposite end of the chip 42 and ispositioned to make electrical contact with a pin 24 of the device 26.The member 44 is substantially parallel to the end 22a of the contact 16which contacts the IC being tested. The parts of contcts from row 16aand ground plane 18a are generally opposed to a like set of pairs ofcontacts from row 16b and ground plane 18b thereby allowing thecontactor assembly 12 to make a reliable electrical connection to all ofthe pins of a DIP IC 26 of the type shown in FIGS. 2 and 3.

The chip device 42, when placed in contact with a pin 24 of the device26 through the member 44, provides a minimum length path to ground. Byinstalling a resistor of appropriate value, the signal line can beparallel terminated (the resistor can have the same resistance as thecharacteristic impedance provided by the contact 16 and its associatedground plane 18). This arrangement both delivers the signal to thedevice under test and eliminates reflections. By installing a chipcapacitor of appropriate value, a substantially zero impedance to groundis provided for the high frequency components of signals on the DUT pin.The total signal path between a device pin and the ground plane is givenby the length of the chip 42 and the contact tip 44, preferably lessthan 0.150 inch. This is a distinct improvement over termination ofreflections and distortions of any known prior art contactor assemblies.With this structure, the length of the decoupling path is equivalent tothe distance recommended for the IC in an operating circuit. Stated inother words, this short signal path to ground from the DUT pin allowsthe testing to very closely simulate the electronic environment of thechip in actual use in a circuit.

Two power pins 24',24' of the IC are connected in parallel with a surgecapacitor 56 through a flexible mounting assembly 50 (shown in FIGS. 2 6and 7) which includes two strips 52 and with at least one integral,vertically extending arms 54. The two arms 54 shown in solid line FIG. 2are soldered to the two power pins 24',24'. The other arm 54 shown inphantom in FIG. 2 indicates how several pins can be shorted through astrip 52 which then acts as a shorting bar. The strips 52 are spacedslightly from each other and bridged by the capacitor 56 whichelectrically connects the strips. The arms 54 are attached at theirupper ends to associated contacts 16 (typically by soldering). Thismount for the surge capacitor 56 enables the system to test theoperation of an IC that causes a large current surge without inducing asignficant change in the ground reference voltage. An advantage of theabove arrangement is that it provides a permanently attached grounddecoupling for the devcie being tested of shorter path length andtherefore of lower impedance than heretofore possible whileaccommodating the flexure movement of the contacts. This results inreductions in ground noise and increases the accuracy of the testresults.

It is also significant that the contactor assembly is surface mounted tothe DUT or contactor board 34 from the front of the contactor assembly,that is, the side adjacent the device 34 and opposite the board 34, andremains attached. With this arrangement, once a contactor assembly ismounted, it is not necessary to separate the contactor from the DUTboard for installation into a test handler. Contactor, DUT board andtest fixture remain an integral unit with contactor fitting over guidepins in the handler. A latch plate mounted on the handler locks thecontactor in place. This in turn means that once signal lines areestablished, they are not broken and re-established as is the case withthe contactor assembly and connection system described in theaforementioned Daymarc '626 and '798 patents.

While this invention has been described with reference to its preferredembodiments, it should be understood that various modfications andalterations will occur to those skilled in the art from the foregoingdetailed description and the drawings. For example, while the connectionarrangement described above uses the angled bottom portions of thecontacts to make electrical connection with conductive portions of amulti-layer board, other arrangements may be used to connect a contactwith an associated pad. Similarly, while the chip capacitors andresistors are described as mounted directly on the ground planes byholders, a variety of other mounting arrangements and electricalconnection systems can be devised. Such modifications and variations areintended to fall within the scope of the appended claims.

What is claimed is:
 1. In a contactor assembly for the high speed,automatic testing of first electronic devices (DUT's) that are packagedwith a line of pins arrayed along at least one side of each of the DUT'swhere the contactor assembly includes a base formed of an insulatingmaterial and a plurality of elongated contacts mounted in said base andarrayed in at least one row with a first end of each contact positionedto make electrical connection with an associated pin of the DUT, saidcontacts being formed of a conductive material and being resilientlyflexible to deform laterally from a first position where the first endsof the contact are spaced from the associated one of said pins to allowan unrestricted movement of the DUT through the contactor to and from atesting position to a second position where the first ends of thecontacts make electrical connection with the associated pins when theDUT is in the testing position, the improvement comprisingat least onesecond electronic device in electrical connection with the DUT throughone or more selected pins where said second electronic device is inclose physical proximity to the DUT during testing and disposed betweenthe DUT and said base, the spacing between said DUT and said seconddevice being substantially less than the length of said contacts, andresilient mounting means for said second electronic device which canaccommodate the movement of said contacts between said first and secondpositions comprising at least two arms formed of a conductive material,each arm having a first portion secured to and in continuous electricalconnection with selected one of said contacts near its first end so thatit is in electrical connection with said contact when it is in both saidfirst and said second positions, said first ends of said mounting meansbeing movable with the associated contact between said first and saidsecond positions and a second portion secured to and in continuouselectrical connection with said second electronic device.
 2. Theimproved contactor assembly of claim 1 wherein said second electronicdevice is a surge capacitor.
 3. The improved contactor assembly of claim2 wherein said at least two arms are each in electrical connection withpower pins of said DUT.
 4. The improved contactor assembly of claim 1wherein said first and second arm positions are formed integrally of aresilient conductive material.
 5. The improved contactor assembly ofclaim 1 wherein at least one of said arms has multiple first armportions each electrically connected to an associated one of said pins.6. The improved contactor assembly of claim 1 wherein said second armportions lie in different planes.